Northwest Dive Club

I have a PST HP120 300bar and 7/8" neck, I might have found a brother for it to double up.
My question is where would I find a 7/8" manifold for them?

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Good luck - they aren't manufactured any longer so the valves are tough to find. You can give a call to John at Northeast Scuba Supply, on occasion he has used ones. Otherwise your best bet is to keep an eye out on Ebay or the tech forums (TDS, etc)

7/8" neck tanks are fine as singles but you won't find a decent non-angled manifold for them anymore (or even one of the lame angled genesis manifolds). They haven't been made in over 10 yrs. If you want doubles you are better off selling the 120 and getting modern 3/4" neck tanks.

Ok, how about sidemounting them?

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My other option is a set of LP98's to double up. Fabers

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I think I have the last 7/8 neck manifold in the WORLD!!!!!!

All due respect to Bob and other local sidemounters but its a bullshit strategy for most of our local boat dives. Nevermind the fact that you won't find a decent local sidemount instructor. And I sidemount plenty - my bailout on CCR and open circuit in caves.

Sell the 120s, then double up the 95s or get a set of hp100s - the queen of local intro doubles. The 120s are massively long on most people anyway, you'd need to be over 6'4" or 6'6" to sidemount them without them banging on your knees with every kick.

With all due respect, there are certainly reasonable applications of sidemount tank configuration on some of our local charter boats. The Ocean Quest in particular is well suited for this. For those who wish a high capacity, fully redundant source of gas that can come out of the water one tank at a time, sidemount is the way to go.

Having said that, I prefer using a set of low pressure doubles such as old steel 72s or Faber 85s for boat diving. They're just heavy coming back up the ladder.

I also use Faber FX120s as singles for boat dives, or take one with me to top off my LP doubles via a transfill whip. The old 3500 psi 120s would be great as top-off tanks, but awfully heavy as doubles or even independent twins.

Two 120s are ghastly heavy coming up a ladder, adding deco bottles isn't gonna happen. And Its worse in sidemount because the weight is dynamic and swinging. Just because you own a 120, and can't get a manifold anymore to double them up, is not a good reason to buy a second one and attempt to sidemount them.

For those of us with RIBs you basically can't dive sidemount at any high current sites because you can't get fully geared up on the tube worth a damn in anything bigger than AL80s. (speaking of, if you really want to sidemout locally, AL80s are a good intro sidemount tank and cost effective)

Doubling 120's??? I would have to agree that this would be super heavy and awkward....(yes I own one)

Ok thanks.

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What are the best sizes of doubles? Im 18 and am a athlete so weight isnt much of an issue for me.

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Also woul LP 104's be hard to find?

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verrinne wrote:What are the best sizes of doubles? Im 18 and am a athlete so weight isnt much of an issue for me.

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Pretty subjective however you will find that HP 100's are a well balanced option for doubles in the PNW.

I would start with Faber LP 85s and work up to double FX 100s later. Either set will be enough to get you in plenty of trouble. Remember that if you're using them for deeper dives, you'll need proper training and a deco bottle of EAN50, at the least.

I've heard that LP104s are nice tanks, but they don't show up around here. They're mainly used in cave country (N. Florida).

Not just 'any' HP100's, the old style 7/8 neck are a bitch to trim out because of their design/buoyancy characteristics - they start super head heavy when you put all that brass on top (manifold & regs) so need to trim them you end up running them low on back in addition to a monster tail weight to keep them even remotely tolerable when less than half full. Not _as_ bad as old 72's but for sure not a delight like the newer 3440 standard neck HP100's.

Of course, as we all know you can do this stuff on the cheap, but the bottom line is, at some point if your plan is to stick with it, take the classes, progress, take the next round of classes and someday down the road do the 'big dog' dives you will need to cough up some $$ not only on gear but on gasses (helium is NOT cheap, not by a long shot). Personally I'd recommend saving you coin and getting a set of dubs that will perform well and learn how to dive them instead of spending the money multiple times and having to compensate for less than ideal equipment which will slow your educational advancement. The right gear makes such a difference... massive difference.

The folks here are giving you great advice, and there are some good sets of dubs kicking around, just be patient.

My old construction foreman used to say...

You can only do it right once, but you can do it wrong many many times.

Ok so I found some LP98's for a good price ill be getting in the next week or two.
And I have been practicing with dub LP85's a friend loanded me.

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Thank you all for the help and opinions, it will be nice to meet you all for a dive sometime.

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ljjames wrote:Not just 'any' HP100's, the old style 7/8 neck are a bitch to trim out because of their design/buoyancy characteristics - they start super head heavy when you put all that brass on top (manifold & regs) so need to trim them you end up running them low on back in addition to a monster tail weight to keep them even remotely tolerable when less than half full.................

To each his own - I actually love my 7/8 PST 100's and find that with a 5lb tail weight they trim out perfectly for me.

Billz, that totally works assuming you have the intrinsic buoyancy to float them with the appropriate sized tail weight to keep them trim at end of the dive without having to compensate by adding additional (on top of swing weight) air to wing.

<the following is not for you Bill, you like them and I'm absolutely not trying to convince you otherwise, i'm just putting it out there for others>

In my case when I have a big enough tail weight (I found 5lbs fine at the start but not enough at end when they get even more tail light) I have too much weight. I was then adding additional air to wing which although not a 'big' problem is just not the most elegant solution since common practice is enough air in wing at the start of the dive so can remain underwater at end of dive. Weighted for 'trim' for second half of gas, they would then start out ass heavy, which of course is easily 'fixable' by putting a bit more air in feet. If, like me, someone dives with a doubles kit that doesn't have ditch-able weight, having to overfill the wing just so i can be trim is kinda contrary to what we are taught about having a balanced kit that can be swum up in the event of a failure. That starts leading people down the mental mastrubatory path of bungied backup wings etc...

I see it as adding complication to a system to solve issues caused by diving something that was simply not ideal for 'me' in the first place. They are FANTASTIC single tanks, I adore them for that purpose. Why do I have them? cause I had a bunch left over from my first round of tech diving in the early 90's and I'm a cheap bastard, and wanted matchy matchy tanks so I wasn't swapping around ballast from set to set, and having to remember which tanks need which

Of course part of it is I'm not tall and I do not have nice long legs to cantilever out or extra body to cover with awesome floaty undergarments. There are so many factors in play, but conventional wisdom is they are not the most widely loved tanks for doubles when compared to more modern steel tanks.

Were they un-divable? Of course not, those tanks took me on loads of sub 200' dives along with a set of double HP 80's (which apparently I survived) and probably have 1000 dives on the lot of them. Do I hate them? No, obviously not, I've got 3 sets.

I consider myself a reasonable enough diver to manage the complexities without eating up additional bandwidth (and also i'm a bit of a honey badger and after a point I really don't care about zero degree trim) Did I enjoy diving other tanks 'more' and stack the deck in my favor for classes? yes. Did I watch people struggle with them to find trim, only to put on a set of newer tanks and just float right into trim? yes.

I only mention this stuff cause personally I hate it when I blunder along and after the fact everyone goes 'oh yeah, didn't anyone tell you that sucked?' I'd prefer to get a few views including negatives and positives, so my blundering is done armed with advice/info that i can then choose to ignore

What tanks would I recommend to someone just starting out? Tanks that don't need excessive tinkering to get them dialed. Basically the tanks folks have already recommended in this thread

Nice post Laura, even though I don't know squat about doubles.

I did not share Laura's experience with my 7/8 neck 100s. After adding my 10# v-weight they trim out nicely and have been diving them for years. Again, what works for one might be a nightmare for another. Give 2 people with same height and weight, the very same gear, and you will likely get two separate results. I found out with SCUBA that many questions have many "right" answers so there is a lot of right information in this thread.

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verrinne wrote:Also woul LP 104's be hard to find?

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Around here yes, forget it. They haven't been made in over a decade (even though they were 3/4" necks).

Great cave diving tanks cause they are heavy as snot. Get something smaller IMHO. Modern hp100s or lp85s with 3/4" necks are ideal as starter doubles.

I can't tell the difference between 7/8" and 3/4" hp100s personally. I have 2 of each and either sidemount them in caves or use them as singles. I suspect the real differences are in those old angled genesis manifolds, lordy those are some heavy valves. Thankfully I ditched all of mine long ago and I'm treating my remaining 7/8" valves with kid gloves as they are irreplaceable now.